Acquired Immune Deficiency Syndrome (AIDS) is a current major health problem. This deadly, disease is caused by the human immune deficiency virus (HIV-1). As of August 1993 about 255,000 AIDS cases have been reported to the Center for Disease control. The targets of the virus are the cells such as human peripheral blood lymphocytes, monocytes/macrophages with virus specific attachment surface proteins (CD4+). The long-term objective of this renewal application is to elucidate the mechanism of action and metabolism of a new series of acyclic nucleoside, phosphonates which have demonstrated broad spectrum antiviral activity both in vitro and in vivo. The phosphonylmethoxy ethyl adenine (PMEA), the lead member of the purine series of compounds, has been shown to be a chain terminator of proviral DNA replication. Phase 1/11 trials of PMEA in HIV-infected patients are underway at various sites in the U.S. The present renewal application proposes basic biochemical studies of PMEA and several other members of the phosphonate analogs, particularly the phosphonylmethoxy propyl (PMP) derivatives which demonstrate increased selectivity against HIV. The specific aims of the proposed work are to: 1)use variants from the human T cell line CCRF-CEM that have a deficiency in the anabolic phosphorylation of PMEA as model for identification and detailed characterization of the enzyme pathway(s) responsible for the activation of the phosphonate analogs, 2) purify and characterize the enzyme(s) from CEM cells and their variants to define the substrate specificity of analog metabolizing enzyme(s), 3) determine the mechanism of activation that is operative for PMEA and its analogs in primary human mononuclear cells, including lymphocytes and monocytes/ macrophages , that are the primary targets for HIV infection, 4) investigate the potential of HIV to develop resistance to the phosphonate analogs and determine the cross-resistance, if any, with HIV strains that carry mutations to existing antiretroviral drugs such as the dideoxynucleosides and non-nucleoside RT inhibitors. The work proposed in this application will address several deficiencies in our under-standing of the cellular metabolism and action of acyclic phosphonate analogs in human lymphoid cells and will contribute to the long-term goal of developing selective chemotherapy against AIDS and associated opportunistic infections using different drug combinations.